I understand, but I'm already using up my mental capacity from just reading the text.
I can't afford to spend my attention in reading it aloud with the rise and fall of the sentences.
ご質問ありがとうございます。
① "I understand, but I'm already using up my mental capacity"＝「分かります、でも既に能力を使い切っています」
"from just reading the text."＝「テキストを読むだけで。」
② "I can't afford to spend my attention"＝「余裕がありません」
"in reading it aloud with the rise and fall of the sentences."＝「文章に抑揚を付けながら声を出して読むことに。」
ご参考に。
アメリカ合衆国 
